Many different types of work machines, such as track type loaders, track type tractors, skid steer loaders, excavators and the like, utilize differential speed control to effect steering of the machine. On these types of work machines, steering is typically accomplished by changing the relative speed between the left and right drive motors associated with such machines. The left drive motor typically controls the speed at which the left track, belt or machine wheels rotate in a fore and aft direction, and the right drive motor typically controls the speed at which the right drive mechanism rotates in the fore and aft direction. Where such drive motors are hydrostatic, the reaction of the work machine to various steering commands can vary depending upon the ground speed of the machine, engine speed, and the available hydraulic flow to the respective drive motors. Generally, the higher the engine speed, the higher the pump flow available to the drive motors. This creates a more responsive, less controllable machine at higher engine speeds.
In addition, the very nature of these types of work machines requires that such machines be used in confined areas such as close to buildings and the like where precise maneuvering is required. Since the gain typically associated with the operator input device that controls the steering of the machine, such as one or more steering control levers or a joystick, is fixed, moving the operator input device a certain displacement will always produce the same steering response regardless of the particular work environment or operating conditions of the machine. For example, in an environment where the particular work machine is working close to a building, a finer or more precise control of the steering command is desirable and large steering corrections may facilitate an unsafe operating condition.
Still further, certain work tools used on certain types of work machines require high engine speed in order to operate the work tool properly. These higher operating engine speeds produce a higher output flow from the hydraulic pump which controls the respective drive motors. As previously explained, this creates a more responsive, less controllable steering command at high engine speeds. As a result, turning the particular work machine will be jerky at best. When these types of work tools are used, it is sometimes very difficult to control the steering of the particular machine, particularly in space limited environments.
It is therefore desirable to provide a steering control system which allows an operator to select different modes of steering and vary the gain of the operator input steering device based upon the particular work environment of the machine, or other sensed conditions of the machine. Under certain conditions, it is also desirable to vary the gain of the operator input steering device based upon the type of tool being utilized on the machine.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.